Preparation Of Polypyrrole Conductive Hydrogel By Interfacial Polymerization And Its Application In Pressure Sensor

Conductive hydrogels are usually produced by compounding hydrogel and conductive materials.With the three-dimensional network structure and electrical conductivity,the conductive hydrogels have been applied in the fields of sensors,capacitor and bioelectrode.However,the traditional preparation method for conductive hydrogel is associated with the issue of poor dispersion of conductive polymer.For instance,for the blending method for preparing the conductive hydrogel,the conductive polymer particles are prone to be agglomerated and sedimented.As for the in-situ polymerization for preparing the conductive hydrogel,the conductive polymer polymerizes on the surface of the gel when the monomer-containing gel is in contact with the initiator solution,which can block the micropores on the surface of the gel,affects the subsequent reaction,and consequently reduce the conductivity of the hydrogels.In ordered to meet the requirement of the application of sensors,the conductive hydrogels should have excellent conductivity,as well as the mechanical properties.In the study,the polyacrylic acid/polypyrrole(PAA/PPy)conductive hydrogel is prepared by interfacial polymerization method.Interfacial polymerization is the polymerization reaction of the conductive polymer,in which the initiator and the conductive polymer monomer are dissolved in the aqueous and the oil phases,respectively,and the oil-water interface is constructed in the pores of the gel.Then,the polyethylene glycol(PEG)and PAA are used to synthesize a double-network hydrogel with interpenetrating structure to improve the mechanical properties of the hydrogel.Thus,the PAA/PEG/PPy composite conductive hydrogel has both excellent mechanical and electrical properties.The double-network structure hydrogels are formed by the penetration of rigid and flexible networks,which have positive effects on the mechanical dissipation,thus the mechanical properties can be finely improved.In addition,the thesis also analyzes the resistance change of PAA/PEG/PPy composite conductive hydrogel under external cyclic stress,and applies it on the motion monitoring for the knuckles and wrist joints.The main contents and results of this thesis are as follows: 1.The first step is to prepare the PAA hydrogel skeleton and then polymerize the PPy in the PAA hydrogel by interfacial polymerization to obtain the PAA/PPy composite hydrogel.According to the tests of Fourier Transform Infrared Spectrometer(FTIR),scanning electron microscope(SEM)and Energy Disperse Spectroscopy(EDS),it indicates that the conductive PPy particles are successfully polymerized in the pores of PPA hydrogel by interfacial polymerization.The compression testing demonstrates that the PPy has very limited effect on the mechanical properties of the composite hydrogels,with the compression moduli between 30 ? 40 KPa.The results of electrical performance testing show that the resistivity of the sample set with 1% Py concentration is 55.293 K? * cm,which is only 1/4 of the sample set without Py(204.842 K?*cm),implying that the PAA/PPy composite conductive hydrogel has excellent electrical performance.2.The PEG and PAA are used to synthesize double-network hydrogelto improve the mechanical property,and prepare the PAA/PEG/PPy composite conductive hydrogel with the method of interfacial polymerization.The compression modulus of the sample group with a PEG concentration of 20% reached 102.172 KPa,which was 3-4 times of that without PEG(31.034kpa).Moreover,the stress is greater than 200 KPa when the strain is 50%(meet the requirement of “greater than 100 KPa”).By regulating the PEG concentration,a series of PAA/PEG/PPy conductive hydrogels with compression modulus of 40-100 KPa can be obtained.The experimental results indicate that PAA/PEG/PPy composite conductive hydrogel has both excellent mechanical and conductive properties.Specifically,the resistivity of sample set with 20% PEG concentration could reach 5.077 K? * cm.3.The PAA/PEG/PPy composite conductive hydrogel is applied for the performance test of pressure sensor.Considering that the sensor should be ensured to has the longterm stability,good recovery performance within the test range and quick response and recovery within the test frequency,different cycle times test,different strain test and different frequency test are conducted through applied cycle stress.The testing results show that PAA/PEG/PPy composite conductive hydrogel has good resistance recovery performance.The results of the finger and wrist motion tests indicate that the PAA/PEG/PPy composite conductive hydrogels are possible to be used for the pressure sensors to monitor body movements.In the study,interfacial polymerization is adopted to successfully polymerize the PPy in the pores of the PAA hydrogel,and composite the PAA/PPy conductive hydrogel with excellent electrical conductivity,which solves the drawback of traditional preparation methods,i.e.,the poor dispersion of PPy.By using PEG and PAA to construct a double-network structure hydrogel,the mechanical properties can be improved and its mechanical properties can reach the test range in the Medium pressure zone,which makes PAA/PEG/PPy composite conductive hydrogel be possible to be applied on the human motion monitoring sensor.However,the mechanism by which the PEG component affects the conductivity of PAA/PEG/PPy hydrogels in this study remains to be further studied.